Aluminum alloy



*Patente cl July 14, 1942 2,290,022 I ALUMINUM ALLOY Walter Bonsack,South Euclid, Ohio, assignor to -The National Smelting Company,Cleveland, Ohio, a corporation 01' Ohio No Drawing. Originalapplications April 17, 1941, Serial No. 389,020 and June 16, 1941,Serial No. 398,315. Divided and this application August 7, 1941, SerialNo. 405,886

6 Claims.

This invention relates-to alloys, and particularly to aluminum basealloys suitable for casting and working, and having high strength atordinary and elevated temperatures. Y

This application is a division of my copending application Serial No.389,020, -filed April 17, 1941, for Aluminum alloys, and of my copendingapplication Serial No. 398,315, filed June 16, 1941, for Aluminumalloys.

It is an object of this invention to produce alloys having relativelyhigh elongation and relatively high tensile strength.

It is a further object of this invention to provide a relatively lightalloy which may be easily cast and machined, which may-be used atelevated temperatures without a rapid deterioration of desirableproperties, and which may be readily treated with anodic treatment togive excellent lustre and finish.

It is a. still further object of this invention to provide an alloyhaving a relatively high proportional limit and relatively high fatiguestrength, and in which these properties may be obtained without heattreatment. I

It has been found that an aluminum alloy containing iron, and havingzinc and magnesium present in proper proportions, will produce an alloythat may be readily cast and have improved physicalproperties for useboth at ordinary and elevated temperatures,v and which may have theseproperties improved by heat treatment.

When magnesium and zinc are added to aluminum in the proper proportions,a ternary comrelative to each other are quite similar in both formulasand for the purposes'of the improved alloy, the magnesium and zincshould be present in about the proportion necessary to form the ternarycompound of either formula.

An excess of zinc, over and above that which cooperates with magnesiumand aluminum to form a ternary compound according to the above formulahaving the greatest proportion of zinc, increases the brittleness anddecreases the duotility of the alloy. 'For this reason it is undesirablethat zinc be present in'quantiti'es substantially greater than theamount to react to form such a ternary compound with magnesium andaluminum. The most desirable properties are obtained when themagnesiumand the zinc are proportioned so that the ratio of magnesium(uncombined with any silicon) to zinc is about equal to the ratiorepresented by the formula nesium may be provided to replenish lossesthat properties, good color, and excellent corrosion resistance. Incalculating the amount of'magnesium and zinc that should be present inthe aluminum alloy to form the desired percentage of ternary compound,only magnesium which is 4 not combined with silicon is to be calculated,as it is only such magnesium that is available to combine with zinc andaluminum to form the ternary compound.

The ternary compoundis said by some investigators to have a compositionhaving substantial- 'ly the formula AlsM'gaZnc, and other investigatorshave considered the formula for the ternary compound as being AlzMgaZm.It will be seen that the amounts of magnesium and ZlnC may occur whenthe alloy metal is remelted.

Magnesium adds tothe hardness and machining qualities of the alloyv and,as above stated, should be present in an amount sufiicient to combinewith the zinc and aluminum present.

In greater quantities magnesium tends to make the alloy sluggish,decreasing castability.

Magnesium and zinc have heretofore been added to aluminum in theproportion represented by the formula MgZnz. It has been found, how;-ever, that a given percentage of ternary compound is more effective inproducing desirablealuminum alloys in an amount of about 2%.

The percentage in solid solution increases at high temperatures and,decreases upon cooling, the excess precipitating out. Aluminum alloyscontaining the ternary compound may, therefore, be advantageously heattreated to improve their properties.

A small amount of silicon is usually present in aluminum alloys and from.15% to about 3% is desirable'in alloys of the present invention whichare to be forged or drawn; more than 37% is frequently desirable incasting alloys. Silicon combines with magnesium in preference to most Asmall amount of magelements, each part by weight of silicon combiningwith about 1.75%, by weight, of magnesium zinc and form the ternarycompound according I to the formula A12Mg3Zn3. MgzSi is more stable thanthe ternary compound above mentioned and may be maintained in solidsolution in aluminum alloys in an amount up to about 1.85%, which is thequantity of MgzSi present if the silicon is present in the alloy, andacts as a hardener, which is sometimes desirable in conjunction with theternary compound. Mgzsi does not, however, make an eflicient use of themagnesium as does the above mentioned ternary compound. Therefore, it isdesirable to have the magnesium present on the rich side to prevent thesilicon from being present in excess and taking magnesium away from theternary compound.

If the alloy is desired particularly for casting purposes, more silicon,such as up to about 1.5%, may be present. If, however, a somewhat largeramount of silicon is present in the alloy than is desirable for thepurpose for which the alloy is intended, and such amount of silicon isnot too excessive, thena small amount of calcium may be added. Calciumhas an even stronger affinity for silicon than has magnesum and,therefore, it can be used to reduce the amount of silicon available forcombination with magnesium. The amount of the relatively expensivemagnesium available for the formation of the ternary compound may thusbe increased. -Although much more than 1.85% silicide acts as asupplemental hardener and more than about 3% or so makes the alloy moresluggish and adversely affects the castability of the alloy, up to 3% isdesirable, and more than 3% may, in some cases, be desirable in theproduction when a large amount of the ternary compound is present in thealloy. Usually, however, the amount of silicon should be between .5% and1.5%, especially in castings not heat treated. This is true even whencalcium'is present, although with the latter element more magnesium isavailable for formation of the ternary compound.

It has-now been found that aluminum alloys containing magnesium (overthat necessary to combine with silicon) and zinc inthe proportions toform a ternary compound are greatly improved by the addition of one ormore mem- .bers of the group of hardening elements, consisting of .l% to1.5% nickel, .1% to 1.5% manganese and .05% to chromium, in a, totalamount of about'.2% or .3% to 5%, with or without one or more of thegrain refining elements selected from the group consisting of titanium,columbium, zirconium, boron, tungsten, molybdenum, tantalum andvanadium, in a total amout of .005% to .5%.

Although the metal manganese, chromium and nickel each increase thehardness of the alloy, 9. given percentage of each of these elementsimproves certain 01' the properties more than it does others. It istherefore preferred/that more than one of these elements be present inthe alloy. Nickel increases the tensile strength.

proportional limit and yield strength of the alloy without decreasingits elongation to any appreciable degree. In fact, with certain amountsof nickel the elongation is increased,

so that an alloy having exceedingly desirable and exceptional propertiesmay be obtained.

Alloys containing nickel may be readily heat treated .or age hardened togive somewhat superior properties, but very desirable properties whichare almost equivalent to the heat treated alloys are also obtained whencastings are simply aged at room temperature, with or without quenchingfrom the mold.

Nickel is quite an effective element in the alloy and appreciableimprovements in properties of the alloy are noted when it is present inan amount of about .1% or more. ferred properties are obtained withabout .3% to about .8% or 1% nickel, and in some cases it is desirableto have the nickel present in amounts as great as 1.5%.

Manganese, although it decreases the tensile strength and elongation tosome degree, increases the yield strength, hardness and proportionallimit of the alloy. It also makes the alloy more corrosion-resistant.

Alloys containing manganese may be readily heat treated or age hardenedto give somewhat superior properties, but very desirable properties areobtainable when castings are simply aged at room temperature, or whenquenched from the mold and aged.

Manganese is a very efiective element in the alloy and desirableimprovements are noted when about .l%, or even a little less, is presentin the alloy. The preferred properties are obtained with about .2% toabout .3% or .8% manganese, and in some cases it is desirable to havethe manganese present in amounts as great as about 1%, or even 1.5%.

Chromium, although it does not appear to improve the proportional limitand yield strength of the alloy, increases its elongation. It is,therefore, particularly advantageous that both chromium and manganese bepresent. As little as 05% or .1% chromium, particularly with manganese,is eifective in improving properties of the alloy, but .2% or .3% toabout .8% or even 1% is desirable. present, the total of manganese andchromium should preferably be between about .3% and v 1.5% of the alloy.When both manganese and metal and a relatively small amount oftemarycompound, or with a relatively small amount of such metal and arelatively large amount of magnesium and zinc in the proportions of aternary compound.

As silicon decreases the ductility of the alloy to a substantial degree,it is best that when the alloy contains nickel present in the upperportion of the above mentioned range the silicon does not exceed .7% or.8%, as the presence of too much of the hardener MgzSi may decrease 'theductility to such an extent that the alloy is undesirable for manypurposes. Alloys containing nickel and free magnesium and zinc in theratio of a ternary compound may contain as much as 1% or 1.5% silicon.-While 2% or 3% of the ternary compound of aluminum, magne- The pre- Whenmanganese is also.

sium and zinc improves the properties of aluminum or aluminum alloyshaving low silicon content, alloys containing such low percentages of aternary compound are relatively dimcult to cast.

An alloy containing 2% of the ternary com-- pound may be used forcasting purposes. The

castability, however, is improved with an increase in the amount .ofternary compound, and it is, therefore-preferred to have a largerpercentage of the ternary compound present, such as 4% to 8%, forcasting purposes. When the casting is more or less intricately shaped,still greater with the lower percentages of the ternary com- I pound.

A larger proportion of the ternary compound and metals of, the abovehardening group may be present in alloys which are to be given asocalled solution treatment than in alloys to be given only an agingtreatment, or those to be quenched from the casting mold and aged atrelatively low temperatures. Thus, the desirable properties of thesolution heat treated alloys may be obtained when they contain theternary compound in amounts up to or so, whereas less of the ternarycompound, such as 4% to 15%, is preferred in alloys which are quenchedupon removalirom the mold and heatv treated at a low temperature, ,oraged at room temperature. v a a i It has generally been considered thataluminum alloys of magnesium containing iron much above the impurityvalue in commercial aluminum are of little commercial value; but it hasalso now been found that an alloy' containing the above describedternarycompound, with or without one 0r moreof the abovementioned groupof harden-' ing" elements, and with or without one or more of the abovegroup of .grain refiners,'is improved by the presence of iron insuitable proportion.

Iron in suitable amounts further increases the hardness and tensilevstrength of the alloy without decreasing its ductility a substantialamount.

'A small amount of iron thus permits one to obtain the propertiesdesired with a smaller amount of magnesium and zinc. These alloyscontaining iron may be readily heat treated or age hardened to givesomewhat superior properties, but

the iron in combination with the ternary elements in the aboveproportion is also outstanding, in that almost as desirable propertiesare 5 obtained when castings are aged at room temperature without a heattreatment or quenching. r

Iron has. generally been considered to crystallize in largeplatelike-crystals, which weaken the alloy. Iron in the presence of theternary compound appears to crystallize in finely dispersed sirable forsome purposes. For most castings it is desirable that the alloy-have .6%or .7% to 1.5% of iron, although about 1% is usually preing ingredientsand upon the amount of ternary present, a given hardness and tensilestrength often being obtainable with a relatively larger amount of ironand a relatively smaller amount of ternary compound, or a relativelysmaller amount of iron and a relativelylarger amount of temary.

The hardening elements and the grain refining elements are particularlydesirable in an aluminum alloy containing both iron and the ternarycompound. Although the iron itself improves the properties of the alloy,the hardening elements and the grain refining elements exert a. stillfurther improvement independently of iron.

The aluminum alloys of the present invention containing magnesium,uncombined with silicon,

and zinc in the proportion of a ternary com- ,a

pound, when cast in molds of a design such that chilling takes placesubstantially simultaneously in the various portions of the casting,solidify without the use of grain refining agents and form goodcastings.However, it has been found that certain grain refining elementssubstantially improve the properties of the aluminum alloy containingthe ternary compound, whether or not it contains one or more of theabove hardening metals, with or without iron. This is especially truewhen the metal is cast inmolds of more or less intricate shape, wherethe chilling may not be so uniform throughout the casting.

Grain refiners which improve the properties of the alloy are boron inthe amount of .005% to 1%, zirconium-in the amount of .01% to .5%,tungsten in theamountof .01% to .5%., molybdenum in the amount of .01%to 25%, vanadium in the amount of .01% to .5%, titanium in the-- amountof .05% to .5%, columbium in the amount of .01% to .5%, and tantalum inthe amount of .05% to .5%. These grain refining elements shouldpreferably be present in a total amount of from .005% to .5%, and it isfrequently desirable to have more than one of these elements peciallytungsten and molybdenum, improve both ferred. The quantity ofirondesired in the alloy depends also-uponthe quantity of otherhardenthe strength and the elongation of the castings. Ofthesatitanium,being less expensive, is usual- 1y used for ordinary castings, but incases where ganese, chromium and nickel, substantially de-.

crease the hot shortness, improve the properties of the alloy, andassist in maintaining the improved properties at high temperatures, suchas are encountered in internal combustion engines. The above grainrefining elements, particularly members of the group consisting oftungsten, molybdenum,-vanadium and titanium, also have this propertywhen present in substantial amounts, such as .2% or .3%, or so. It is,therefore, especially desirable to have upto .5% or so of these latterelements present when other hardening ingredients are absent.

EXAMPLE 1 Test bars chill cast from an alloy containing 6% of theternary compound, about .6% iron, about 25% chromium, and about .5%manganese, showed, after quenching and aging for seven days at roomtemperature, a tensile strength of 41,600 lbs/sq. in., a yield strengthof 23,500 lbs/sq. in., a proportional limit of 17,600

lbs/sq. in., an elongation of 9.6%, and a hardness of 80 kg./mm

When bars of the same alloy were simply aircooled and aged for' sevendays at room temperature, the tensile strength was 41,600 lbs/sq. in.,the yield strength was 23,500 lbs/sq. in., the proportional limit was18,100 lbs/sq. in., the elongation was about 8%, and the hardness was 82kg./mm

When the quantity of manganese in the alloy of Example 1 was inc: easedto about 1%, the tensile strength of air-cooled test bars, aged forseven days at room temperature, was 38,900 lbs/sq. in., the yieldstrength was 26,600 lbs/sq. in., the proportional limit was 20,100lbs/sq. in., the elongation was about 5%, and the hardness was 82 kg./mm

From the above examples it is seen that even a small proportion ofmanganese and chromium markedly increases the tensile strength,proportional limit, yield strength, hardness, and even the elongation ofaluminum base alloys. Since most alloying elements which tend to improvethe tensile strength of an alloy also usually de crease its elongationto a marked degree, it is seen that manganese and chromium incombination with each other and with a ternary compound have aremarkable efiect, and that an alloy of outstanding characteristics isproduced.

An aluminum base alloy containing .2% silicon and magnesium (uncombinedwith silicon) and zinc in the proportions represented by the formulaAlaMgrZns, and in sufficient amounts to produce 6% of this ternarycompound in the alloy, was prepared. From this base alloy threedifferent alloys were prepared .by incorporating the proportions of ironindicated in the following Table 1, and chill cast in standard test barmolds. Several bars of each alloy were given the indicated heattreatments, that is, some of the bars of each alloy were removed fromthe mold while hot and allowed to cool in air, and then aged seven daysat room temperature; another set of bars was removed from the moldbefore the bars had cooled sufliciently to precipitate the hardeningingredients, then quenched in water and al- Alloy air-cooled; aged atroom temperature seven days. "Alloy quenched; aged at room temperatureseven days.

It is seen from the test results of the above table that, although thetensile strength may be increased to some extent by aquenching'treatment, almost-equal results are obtained by-'sim-' plyair-cooling the casting and aging it at room temperature. Before thequenched casting is aged a tensile strength of over 30,000 lbs/sq. in.is obtained, while at the same time the casting has an elongation of12%. In an aged casting a tensile strength of even greater than 40,000

lbs/sq. in., together with an elongation of almost 8% is obtained. In anaged casting maximum elongation and substantially maximum strengthfareobtained when the iron content is about 1% or so.

When the quantity of ternary compound is increased, these maximum valuesmay be obtained with a somewhat lower iron content, or higher maximumstrength is obtained with the same iron content; the castability of thealloy may be also somewhat increased. It will be seen that, since theiron permits one to obtain exceptionally high elongation, combined withhigh tensile strength, without the necessity of even as much heattreatment as quenching from the mold, the alloy is especially useful formany purposes, such as large castings or forgings, wherein it isdiflioult to heat treat or quench.

As shown above, iron and the ternary compound alone produce exceptionalproperties in an aluminum base alloy, with or without the usualimpurities. Even more desirable properties, for some purposes, areobtained with iron and one or more hardening metals of the groupconsisting of about .1% to 1.5% chromium, about .05% to 1.5% manganese,and about .l% to 1.5% nickel. As little as a total of about .l% or .2%of these hardening metals is effective in improving the iron ternaryaluminum alloy,- but about .4%' or .5% to about 1.5% of these hardeningmetals is preferred, and even 2% is desirable for many applications.'The'iron may be present in the amounts above set forth, but less thanabout 1.5% is preferred.

If it is desirable to make the alloy more responsive to heat treatment,from .2% to about or even up to about 1.5% copper may be present in thealloy. Copper is a precipitation hardening ingredient, and the benefitsof this element are obtainable when the alloy is subjected to conditionsof heat treatment which precipitate the element from the solid solution.The presence of from .5% to 1.5% copper permits a reduction in theamount of the ternary compound, which may be as low as 1%, andpreferably should not exceed about 10% or 12%.

When copper is present in the above alloy containing magnesium in theproportion to combine with the silicon to form MgzSi, and with the zincand aluminum to form a ternary compound as above described, iron, asabove set forth, may or may not be present, although superior propertiesare obtained with .4% to 1.5% or 2% iron. The alloys containing copperand iron are substantially improved when at least one member of theabove group of hardening elements and/or at least one member or thegroup of grain refining elements are also present.

EXAMPLE 2 chromium, about .2% silicon, and about .2% titanium, was chillcast into test bars, quenched and aged three hours at 125 C. When testedthese bars had the following properties: tensile strength 43,500 lbs/sq.in.; yield strength 35,400 lbs/sq. in.; proportional limit of 23,500lbs/sq.

in.; elongation of 6.5%; and hardness of 86 Rockwell E.

ExAMrLr': 3

The alloy of Example 2, but containing '.75%

copper in addition to the elements thereof, when chill cast into testbars, quenched and ,aged

three hours at 125 0., had the following properties: tensile strength43,000 lbs/sq. in.; yield strength 31,400 lbs/sq. in.; proportionallimit of 19,500 lbs/sq. in.; elongation of 5.3%; and hardness of 86Rockwell E. r 1

EXAMPLE 4 The alloy of Example 2, but containing 1% copper in additionto the elements thereof, when chill cast into test bars, quenched andaged three hours at 125 0., had the following properties: tensilestrength of 40,200 lbs/sq. in.; yield strength 33,100 lbs/sq. in.-;proportional limit of 17,300 lbs/sq. in.; elongation of 3.2%; andhardness of 83 Rockwell E.

Since the molecular proportion of zinc is never the following tableshowing the improvement in an alloy containing a small percentage ofsilicon,

' about 6% ternary compound, about 1% iron, and

about .2% titanium. The test bars were chill cast, quenched from'themold, and tested after aging at room temperature for the periodindicated.

To obtain these exceptional properties in aluminum base alloys commonlyin use one has to resort to a solution and aging heat treatment.

more than the molecular proportion of'the relativelylight magnesium inthe ternary compound,

it is seen that, in addition to high strength, the alloys are light inweight-and are, therefore; especially adapted to aircraft constructionandv the like. This is particularly true when the quantity of ternarycompound is sufiiciently low so that the alloy may be drawn or rolledinto structural members. v

If the alloy contains uncombined silicon, about 1.75% magnesium isrequired to combine with each percent of uncombinedsilicon to formmagnesium silicide (MgzSi) before any ternary compound will be formed.For example, if 2% of the ternary compound on the basis of A-lzMgaZIn bedesired in an alloy having .3% silicon, the

amount of magnesium to be added to form the whereas in alloys of thepresent invention it is not pecesary to solution heat treat forimprovement in properties.

The alloys of the present invention have good fatigue and tensilestrength and a relatively high proportional limit, even at relativelyhigh temperatures; they may be heat treat'ed to improve and modify theirproperties; and they have 'sufficient'ductility and hardness so thatthey can be used as sheets, rods, wire. structural shapes, castings,machine, parts, etc. These alloys have a desirable color, high corrosionresistance, and may be anodically finished or highly polished withexcellent results, and are suitablefor many uses, among them being theproduction of castings which are shaped or formed to some extent aftercasting. The alloys having the lower percentages of ternary compound mayeven be forged It is to be understood that, in considering the i amountof zinc and magnesium to add to aluthe zinc in the ranges of theformulas given for the ternary compound. The proportions for theformation of the ternary compound in the alloy exist when the magnesium,is about to of the zinc content plus 175% ofthe silicon content. Mostdesirable properties may be obtained when the magnesium (uncombined withsilicon) is in the lower portion of this range, or about 35% to 40% ofthe zinc.

-In the above examples of alloys of the present that the tensilestrength may increase up to approximately of its initial value by agingminum alloys to form the ternary compound of aluminum, magnesium andzinc in the alloy, such magnesium as is necessary to combine with theuncombined silicon is not to be considered as part of" the magnesiumnecessary to form the specified 'amount of ternary compound.

It is to be understood that the particular compounds disolosed andthe-procedure set forth are 1 presented for purposes of explanation andillusat room temperature for relatively long periods 1 of time, such asa few months. The same improvement in tensile strength can, ofcourse,lbe

tration, and thatvarious equivalents can be used and modifications ofsaid procedure can be'madewithout departing from my invention as definedin the appended claims.

What I claim is:

1 An aluminum alloy containing magnesium, zinc, about .4% to 2% iron,about .2% to 1.5% copper, silicon in an amount up to 1.5%, and one ormore metals of the hardeners and grain refiners to increase strength,ductility or'hardness of the-alloy, with the balance substantially allaluminum and minor impurities, the amount of zinc in the alloy beingabout .6% to 12%, and the amount of magnesium in the alloy uncombinedwith the siliconbeing about 35% to 45% of the zinc content, the totalmagnesium being within the range of about .5% to 7%.

2. An aluminum alloy containing magnesium,

The improvement of properties is illustrated by a zinc, about .4% to 2%iron, about .2% to 1.5% copper, silicon in an amount up to 1.5%, and oneor more metals of the hardeners and grain refiners to increase strength,ductility or hardness of the alloy, no one of such metals being presentin amounts more than 1.5%, with the balance substantially all aluminumandminor impurities, the amount of zinc in the alloy being about 1.2% to7.2%, and the amount of magnesium in the alloy uncombined withthesilicon being about 35% to 45% of the zinc content, the totalmagnesium being within the range of about .5% to 7 3. An aluminum alloycontaining magnesium, zinc, about .4% to 2% iron, about .2% to 1.5%

, copper, silicon in an amount up to 1.5%, and one or more metals of thehardeners and grain refiners to increast strength, ductility or hardnessof the alloy, no one of such metals'being present in amounts more than1.5%, with the balance substantially all aluminum and minor impurities,the amount of zinc in the alloy being about .6% up to about 6%,"and theamount of magnesium in the alloy uncombined with the silicon being about35% to 45% of the zinc content, the total magnesium being within therange of about 5% to 6%. v

4. The alloy set forth in claim 3 in which the zinc content is about .6%to 4.8% and the mag.- nesium content is within the range of about 5% to5%.

5. The alloy set forth in claim 3 in which manganese is present in theamount of about .1% to 1.5%.

6. The alloy set forth in claim 3 in which nickel is present in theamount of about .1% to 1.5%.

WALTER BONSACK.

